Benign enlargement of the prostate occurs, to a greater or lesser degree, in every male after the age of 40, but only causes trouble in about 10%. It does so by increasing the outflow obstruction from the bladder, which results in alterations in the structure and physiology of the detrusor which can easily be recognised by urography, and are by no means correlated with symptoms, or with the size of the gland. Since neglect of the consequences of obstruction multiplies the mortality of prostatectomy – e.g., uraemia, retention, and infection – it is important to attempt to recognise it at its earliest state, and equally important to ensure that identical symptoms are not caused by alterations in renal tubular function, neuropathy, diabetes, etc.